How to apply two different materials in Blender Internal on front faces and back faces, *while involving transparency*
I'm not having this issue.
Use the Backfacing output of a Geometry node to drive the Fac input of a mix shader. The top Shader input is what will show up on the front face and the bottom Shader input is what will be on the back face.
Also, I enabled Alpha Clipping on the front face material in the material Settings panel. Backface culling is also turned off for the front face material.